Semiconductor substrate cleaning

ABSTRACT

Methods for removing titanium-containing layers from a substrate surface where those titanium-containing layers are formed by chemical vapor deposition (CVD) techniques. Titanium-containing layers, such as titanium or titanium nitride, formed by CVD are removed from a substrate surface using a sulfuric acid (H 2 SO 4 ) solution. The H 2 SO 4  solution permits selective and uniform removal of the titanium-containing layers without detrimentally removing surrounding materials, such as silicon oxides and tungsten. Where the titanium-containing layers are applied to the sidewalls of a hole in the substrate surface and a plug material such as tungsten is used to fill the hole, subsequent spiking of the H 2 SO 4  solution with hydrogen peroxide (H 2 O 2 ) may be used to recess the titanium-containing layers and the plug material below the substrate surface.

This application is a Divisional of U.S. application Ser. No.10/342,853, filed Jan. 15, 2003 which application is a Divisional ofU.S. application Ser. No. 09/388,660, filed Sep. 2, 1999 which isincorporated herein.

FIELD OF THE INVENTION

The present invention relates to semiconductor substrate cleaning oretching methods used in the fabrication of semiconductor devices. Moreparticularly, the present invention pertains to a method for removingchemical vapor deposition (CVD) titanium and titanium nitride on asemiconductor substrate surface.

BACKGROUND OF THE INVENTION

Many electronic systems include a memory device, such as a DynamicRandom Access Memory (DRAM), to store data. A typical DRAM includes anarray of memory cells. Each memory cell includes a capacitor that storesthe data in the cell and a transistor that control access to the data.The capacitor typically includes two conductive plates separated by adielectric layer. The charge stored across the capacitor isrepresentative of a data bit and can be either a high voltage or a lowvoltage. Data can be stored in either the memory cells during a writemode, or data may be retrieved from the memory cells during a read mode.The data is transmitted on signal lines, referred to as digit lines,which are coupled to input/output (I/O) lines through transistors usedas switching devices. Typically, for each bit of data stored, its truelogic state is available on an I/O line and its complementary logicstate is available on an I/O complement line. Thus, each such memorycell has two digit lines, a digit and digit complement.

Typically, the memory cells are arranged in an array and each cell hasan address identifying its location in the array. The array includes aconfiguration of intersecting conductive lines and memory cells areassociated with the intersections of the lines. In order to read from orwrite to a cell, the particular cell in question must be selected, oraddressed. The address for the selected cell is represented by inputsignals to a word line decoder and to a digit line decoder. The wordline decoder activates a word line in response to the word line address.The selected word line activates the access transistors for each of thememory cells in communication with the selected word line. The digitline decoder selects a digit line pair in response to the digit lineaddress. For a read operation the selected word line activates theaccess transistors for a given word line address, and data is latched tothe digit line pairs. In order for there to be memory cells there mustbe a semiconductor fabrication process which produces a variety of thinfilms.

A large variety of thin films are used in the fabrication ofsemiconductor devices. Chemical vapor deposition (CVD) is a widely usedmethod for depositing such thin films for a large variety of materials.In a typical CVD process, reactant gases (often diluted in a carriergas) enter a reaction chamber containing a deposition surface. The gasmixture may be heated by absorbing radiation as it approaches thedeposition surface. Near the surface, thermal, momentum and chemicalconcentration boundary layers form as the gas stream heats, slows downdue to viscous drag, and changes in chemical composition. Heterogenousreactions of the source gases or reactive intermediate species (formedfrom homogenous pyrolysis) occur at the deposition surface, thus formingthe deposited material. Gaseous reaction by-products are thentransported or vented out of the reaction chamber.

Another popular technique for depositing thin films is physical vapordeposition (PVD). PVD processes deposit thin films on a substrate bysuch techniques as sputtering, vacuum deposition, or laser ablation froma solid source or target having the desired composition of the depositedfilm.

Because of a fundamental difference between CVD and PVD processes, i.e.,gaseous reactants versus solid sources, the resulting films tend to havedifferent chemical characteristics even when the desired resultant filmis the same, e.g., a titanium or titanium nitride film produced by CVDor PVD. These differing chemical characteristics often lead todifferences in how the resultant films react to downstream processing,such as etching, or cleaning, of the substrate surface.

Cleaning of the substrate surface is often desirable after some bulkremoval of material from the substrate surface. As an example, materialcontaining one or more layers may be formed on a substrate surface tofill a hole or recess. A chemical-mechanical planarization (CMP)technique may be used to abrade the material from the surface,substantially leaving only that portion of the material contained in thehole or recess. CMP techniques must be tightly controlled to remove allof the surface material without detrimentally abrading away thesubstrate surface. This often results in patches or islands of thematerial remaining on the substrate surface. Such patches or islands aretypically cleaned from the substrate surface by some chemical etchant.In the case of forming contacts, vias or interconnects in a hole orrecess, removal of such islands is desirable to reduce the risk ofelectrical shorts.

Hydrofluoric acid (HF)-based solutions are popular chemical etchants insemiconductor processing. While such HF-based solutions are generallyeffective at uniform removal of titanium-containing films deposited byPVD processes, they generally result in pitting of titanium-containingfilms deposited by CVD processes. There is a need in the art foralternative methods for removing the CVD titanium and/or CVD titaniumnitride.

SUMMARY OF THE INVENTION

The present invention addresses the above-mentioned problems in the artand other problems which will be understood by those skilled in the artupon reading and understanding the present invention. The presentinvention includes methods for removing a layer of titanium-containingfilm from a semiconductor substrate and apparatus produced using themethods.

One embodiment comprises the removal of a layer of titanium-containingfilm from a substrate surface. The titanium-containing film is removedfrom the substrate by applying a solution of H₂SO₄ to the substratesurface.

Another embodiment includes a method of forming a semiconductorstructure. The method includes forming an insulator layer on a baselayer, patterning the insulator layer to define a hole and forming atleast one titanium-containing layer overlying the surface of theinsulator layer and the sidewalls and bottom of the hole by chemicalvapor deposition. The method further includes forming a plug layeroverlying the at least one titanium-containing layer and filling thehole, removing a portion of the plug layer overlying the surface of theinsulator layer and removing a portion of the at least onetitanium-containing layer overlying the surface of the insulator layerby exposing the portion of the at least one titanium-containing layer toa sulfuric acid solution.

A further embodiment includes a method of forming a semiconductorstructure. The method includes forming an insulator layer on a baselayer, patterning the insulator layer to define a hole, forming atitanium layer overlying the surface of the insulator layer and thesidewalls and bottom of the hole by chemical vapor deposition andforming a titanium nitride layer overlying the titanium layer bychemical vapor deposition. The method further includes forming atungsten layer overlying the titanium nitride layer and filling thehole, removing a portion of the tungsten layer overlying the surface ofthe insulator layer and removing a portion of the titanium and titaniumnitride layers overlying the surface of the insulator layer by exposingthe portion of the titanium and titanium nitride layers to a sulfuricacid solution.

The invention further includes methods of varying scope as well asapparatus produced using the methods of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1H are cross-sectional views of a semiconductor structure atvarious processing stages.

FIG. 2 is a cross-sectional view of a portion of a memory device.

FIG. 3 is a block diagram of an integrated circuit memory device.

FIG. 4 is an elevation view of a wafer containing semiconductor dies.

FIG. 5 is a block diagram of an exemplary circuit module.

FIG. 6 is a block diagram of an exemplary memory module.

FIG. 7 is a block diagram of an exemplary electronic system.

FIG. 8 is a block diagram of an exemplary memory system.

FIG. 9 is a block diagram of an exemplary computer system.

DESCRIPTION OF THE DRAWINGS

In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, like numerals describesubstantially similar components throughout the several views. Theseembodiments are described in sufficient detail to enable those skilledin the art to practice the invention. Other embodiments may be utilizedand structural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention.

The terms wafer and substrate used in the following description includeany base semiconductor structure. Both are to be understood as includingsilicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI)technology, thin film transistor (TFT) technology, doped and undopedsemiconductors, epitaxial layers of a silicon supported by a basesemiconductor structure, as well as other semiconductor structures wellknown to one skilled in the art. Furthermore, when reference is made toa wafer or substrate in the following description, previous processsteps may have been utilized to form regions/junctions in the basesemiconductor structure, and terms wafer or substrate include theunderlying layers containing such regions/junctions. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims.

The method of substrate cleaning will be illustrated in the context ofthe formation of a contact in a semiconductor device. It will beapparent that other semiconductor structures may be formed and utilizedwith the invention.

In order to manufacture a contact in a substrate 20, as illustrated inFIG. 1 A, an insulator layer 12 is formed on a substrate base layer 11and a contact hole 14 is patterned or etched through the insulator layer12 to expose a portion of the underlying base layer 11. Insulator layer12 may be any insulative material, but is commonly a silicon oxidematerial, such as silicon dioxide or borophosphosilicate glass (BPSG).Contact hole 14 has sidewalls defined by insulator layer 12 and a bottomdefined by the exposed portion of base layer 11.

A dielectric anti-reflection coating (DARC) layer 13 optionally may beformed on top of the insulator layer 12 prior to patterning the contacthole 14. Such DARCs improve the resolution of photolithographictechniques utilized to pattern the contact hole 14 and such use is wellunderstood in the art. Additionally, the bottom of contact hole 14 maybe etched or cleaned by a pre-metal deposition cleaning process toimprove the electrical contact to the base layer 11.

As shown in FIG. 1B, chemical vapor deposition (CVD) is then used toform a first CVD titanium-containing layer 15, such as titanium. CVDpermits accurately controlled formation of films, including conformalfilms. CVD titanium layer 15 is formed over the surface of insulatorlayer 12, as well as the sidewalls and bottom of contact hole 14. Avariety of gaseous reactants may be used to form CVD titanium layer 15as is well known by persons skilled in the art.

Referring to FIG. 1C, a second CVD titanium-containing layer 16, such astitanium nitride, may be formed by a second CVD process on CVD titaniumlayer 15. A CVD titanium nitride layer 16 is useful in improvingadhesion to CVD titanium layer 15 of subsequent plug materials used forthe core of the contact. As with CVD titanium layer 15, CVD titaniumnitride layer 16 is formed overlying the surface of insulator layer 12,as well as the sidewalls and bottom of contact hole 14.

The substrate may be annealed to form a titanium silicide interfacebetween CVD titanium layer 15 and the base layer 11, where the baselayer 11 contains silicon. Such silicide interfaces reduce resistancebetween a silicon base layer 11 and CVD titanium layer 15. A rapidthermal processing (RTP) annealing process may be used to form thetitanium silicide interface. The annealing process may include heatingthe substrate 20 to a temperature of approximately 600 to 800 degreesCelsius for approximately 10 seconds. The annealing process may beperformed at any time after forming CVD titanium layer 15.

Referring to FIG. 1D, a plug layer 17, such as tungsten, is deposited onCVD titanium nitride layer 16. Plug layer 17 may contain materials otherthan tungsten, particularly other metals when forming a contact.However, the material of plug layer 17 must be generally resistant tosulfuric acid (H₂SO₄), as will become apparent below. Referring to FIG.1E, the overriding tungsten layer 17 is removed from the top of thesubstrate by using a chemical mechanical planarization (CMP) process toform contact 24. CMP processing often utilizes changes in frictionbetween an abrading surface and the surface of the material beingabraded. This relative friction technique can permit use of theinsulator layer 12 as a stopping layer. An alternate method ofdetermining a stopping layer is to simply abrade for a defined period oftime, having previously determined the amount of time necessary to reachthe stopping layer. In either case, because of the inherent variabilityin industrial processing, residual material is often left behind on thestopping layer.

As shown in FIG. 1E, such residual material may take the form of islands22 on the surface of substrate 20. Note that as FIG. 1E is notnecessarily drawn to scale, the slope of islands 22 may be exaggerated.Because these islands 22 contain conductive material, i.e., CVD titaniumlayer 15 and CVD titanium nitride layer 16, they may result inundesirable electrical shorts if they are not removed. Such removal isaddressed by the various embodiments of the invention.

In one embodiment, the substrate 20 and accompanying layers are immersedin a sulfuric acid (H₂SO₄) solution to remove the titanium-containinglayers, i.e., CVD titanium layer 15 and CVD titanium nitride layer 16.Sulfuric acid solution, as used herein, will describe a solutionconsisting essentially of aqueous or anhydrous H₂SO₄ unless notedotherwise by subsequent spiking or additions to the solution. In afurther embodiment, the substrate 20 and accompanying layers are exposedto H₂SO₄ vapors to remove the titanium-containing layers. In a stillfurther embodiment, the substrate 20 and accompanying layers are sprayedwith an H₂SO₄ solution. In one embodiment, the H₂SO₄ solution is heated.In another embodiment, the H₂SO₄ solution is heated to a temperature ofapproximately 100-140° C. In a further embodiment, the H₂SO₄ solution isheated to a temperature of approximately 120° C. In one embodiment, theH₂SO₄ solution is anhydrous H₂SO₄. In another embodiment, the H₂SO₄solution is an aqueous solution containing greater than approximately75% H₂SO₄. In a further embodiment, the H₂SO₄ solution is an aqueoussolution containing greater than approximately 1% H₂SO₄.

In the various embodiments, titanium-containing layers are selectivelyand uniformly removed from the surface of substrate 20 withoutdetrimentally removing surrounding materials, such as tungsten layer 17or insulator layer 12. The surface of substrate 20 includes the surfaceof DARC layer 13 or the surface of insulator layer 12 if no DARC layer13 is present. FIG. 1F depicts the substrate 20 with resultant contact24 following removal of CVD titanium layer 15 and CVD titanium nitridelayer 16.

Following removal of the titanium-containing layers, islands of DARC maystill remain if a DARC layer 13 was utilized in the formation of thecontact 24. To remove residual DARC, a solution of tetramethylammoniumfluoride (TMAF) and HF may be used. In one embodiment, the TMAF/HFsolution is approximately 5-50 wt % TMAF and approximately 0.02-20 wt %HF in aqueous solution. In another embodiment, the TMAF/HF solution isapproximately 22.8 wt % TMAF and approximately 0.28 wt % HF in aqueoussolution. In a further embodiment, tetramethylammonium hydroxide (TMAH)replaces the TMAF. FIG. 1G depicts the substrate 20 following removal ofDARC layer 13.

In some situations, it may be desirable to recess the materials in thecontact hole 14 or otherwise condition the surface of the materials. Inuse with the various embodiments, the H₂SO₄ solution may be spiked withhydrogen peroxide (H₂O₂) which may selectively remove some CVD titaniumlayer 15 and/or CVD titanium nitride layer 16 from the contact hole 14.Spiking the H₂SO₄ solution with H₂O₂ in the present example will resultin recessing of the CVD titanium layer 15, the CVD titanium nitridelayer 16 and the tungsten layer 17 below the surface of the substrate20, along with surface conditioning of tungsten layer 17. FIG. 1Hdepicts the substrate 20 following recessing of CVD titanium layer 15,CVD titanium nitride layer 16 and tungsten layer 17. Recessing may beaccomplished by immersing the substrate 20 in the solution of H₂SO₄ andH₂O₂ for a period of about 2-120 seconds.

Those skilled in the art recognize that semiconductor structures such ascontact 24 are utilized in the formation of more complex integratedcircuitry. As one example, contact 24 may be used as a bit-line contactin a memory device.

Memory Devices

FIG. 2 is a cross-sectional view of one such memory device. The memorydevice includes an array of memory cells. The memory cells includecapacitors 230, access transistors 240, wordlines 250 and bit-linecontacts 260 formed over a base layer 210, often a silicon base layer.Those skilled in the art will recognize that wordlines 250 in FIG. 2 arecoupled to access transistors 240 outside the plane of FIG. 2. Bit-linecontact 260 is used to couple the capacitors 230 to a bit line or digitline (not shown) of the memory device. Bit-line contact 260 may beformed in conjunction with an embodiment of substrate cleaning describedabove. As such, bit-line contact 260 may contain a CVD titanium layer15, a CVD titanium nitride layer 16, and a tungsten layer 17 aspreviously described.

FIG. 3 is a simplified block diagram of a memory device according to oneembodiment of the invention. The memory device 300 includes an array ofmemory cells 302, address decoder 304, row access circuitry 306, columnaccess circuitry 308, control circuitry 310, and Input/Output circuit312. The memory can be coupled to an external microprocessor 314, ormemory controller for memory accessing. The memory receives controlsignals from the processor 314, such as WE*, RAS* and CAS* signals. Thememory is used to store data which is accessed via I/O lines. It will beappreciated by those skilled in the art that additional circuitry andcontrol signals can be provided, and that the memory device of FIG. 3has been simplified to help focus on the invention. At least one of thememory cells has a bit-line contact formed in accordance with theinvention. It will be recognized that other contacts, vias andinterconnects may be used in conjunction with a portion of memory device300 and formed in accordance with the invention.

It will be understood that the above description of a DRAM (DynamicRandom Access Memory) is intended to provide a general understanding ofthe memory and is not a complete description of all the elements andfeatures of a DRAM. Further, the invention is equally applicable to anysize and type of memory circuit and is not intended to be limited to theDRAM described above. Other alternative types of devices include SRAM(Static Random Access Memory) or Flash memories. Additionally, the DRAMcould be a synchronous DRAM commonly referred to as SGRAM (SynchronousGraphics Random Access Memory), SDRAM (Synchronous Dynamic Random AccessMemory), SDRAM II, and DDR SDRAM (Double Data Rate SDRAM), as well asSynchlink or Rambus DRAMs and other emerging DRAM technologies.

As recognized by those skilled in the art, memory devices of the typedescribed herein are generally fabricated as an integrated circuitcontaining a variety of semiconductor devices. The integrated circuit issupported by a substrate. Integrated circuits are typically repeatedmultiple times on each substrate. The substrate is further processed toseparate the integrated circuits into dies as is well known in the art.

Semiconductor Dies

With reference to FIG. 4, in one embodiment, a semiconductor die 710 isproduced from a wafer 700. A die is an individual pattern, typicallyrectangular, supported by a substrate or base layer and containingcircuitry, or integrated circuit devices, to perform a specificfunction. At least one of the integrated circuit devices has asemiconductor structure formed in accordance with the invention. Asemiconductor wafer will typically contain a repeated pattern of suchdies containing the same functionality. Die 710 may contain circuitryfor the inventive memory device, as discussed above. Die 710 may furthercontain additional circuitry to extend to such complex devices as amonolithic processor with multiple functionality. Die 710 is typicallypackaged in a protective casing (not shown) with leads extendingtherefrom (not shown) providing access to the circuitry of the die forunilateral or bilateral communication and control.

Circuit Modules

As shown in FIG. 5, two or more dies 710 may be combined, with orwithout protective casing, into a circuit module 800 to enhance orextend the functionality of an individual die 710. Circuit module 800may be a combination of dies 710 representing a variety of functions, ora combination of dies 710 containing the same functionality. One or moredies 710 of circuit module 800 contain at least one semiconductorstructure formed in accordance with the invention.

Some examples of a circuit module include memory modules, devicedrivers, power modules, communication modems, processor modules andapplication-specific modules, and may include multilayer, multichipmodules. Circuit module 800 may be a subcomponent of a variety ofelectronic systems, such as a clock, a television, a cell phone, apersonal computer, an automobile, an industrial control system, anaircraft and others. Circuit module 800 will have a variety of leads 810extending therefrom and coupled to the dies 710 providing unilateral orbilateral communication and control.

FIG. 6 shows one embodiment of a circuit module as memory module 900.Memory module 900 contains multiple memory devices 910 contained onsupport 915, the number depending upon the desired bus width and thedesire for parity. Memory module 900 accepts a command signal from anexternal controller (not shown) on a command link 920 and provides fordata input and data output on data links 930. The command link 920 anddata links 930 are connected to leads 940 extending from the support915. Leads 940 are shown for conceptual purposes and are not limited tothe positions shown in FIG. 6.

Electronic Systems

FIG. 7 shows an electronic system 1000 containing one or more circuitmodules 800. Electronic system 1000 generally contains a user interface1010. User interface 1010 provides a user of the electronic system 1000with some form of control or observation of the results of theelectronic system 1000. Some examples of user interface 1010 include thekeyboard, pointing device, monitor or printer of a personal computer;the tuning dial, display or speakers of a radio; the ignition switch,gauges or gas pedal of an automobile; and the card reader, keypad,display or currency dispenser of an automated teller machine. Userinterface 1010 may further describe access ports provided to electronicsystem 1000. Access ports are used to connect an electronic system tothe more tangible user interface components previously exemplified. Oneor more of the circuit modules 800 may be a processor providing someform of manipulation, control or direction of inputs from or outputs touser interface 1010, or of other information either preprogrammed into,or otherwise provided to, electronic system 1000. As will be apparentfrom the lists of examples previously given, electronic system 1000 willoften contain certain mechanical components (not shown) in addition tocircuit modules 800 and user interface 1010. It will be appreciated thatthe one or more circuit modules 800 in electronic system 1000 can bereplaced by a single integrated circuit. Furthermore, electronic system1000 may be a subcomponent of a larger electronic system.

FIG. 8 shows one embodiment of an electronic system as memory system1100. Memory system 1 100 contains one or more memory modules 900 and amemory controller 1110. Memory controller 1110 provides and controls abidirectional interface between memory system 1100 and an externalsystem bus 1120. Memory system 1100 accepts a command signal from theexternal bus 1120 and relays it to the one or more memory modules 900 ona command link 1130. Memory system 1100 provides for data input and dataoutput between the one or more memory modules 900 and external systembus 1120 on data links 1140.

FIG. 9 shows a further embodiment of an electronic system as a computersystem 1200. Computer system 1200 contains a processor 1210 and a memorysystem 1100 housed in a computer unit 1205. Computer system 1200 is butone example of an electronic system containing another electronicsystem, i.e., memory system 1100, as a subcomponent. Computer system1200 optionally contains user interface components. Depicted in FIG. 9are a keyboard 1220, a pointing device 1230, a monitor 1240, a printer1250 and a bulk storage device 1260. It will be appreciated that othercomponents are often associated with computer system 1200 such asmodems, device driver cards, additional storage devices, etc. It willfurther be appreciated that the processor 1210 and memory system 1100 ofcomputer system 1200 can be incorporated on a single integrated circuit.Such single package processing units reduce the communication timebetween the processor and the memory circuit.

Conclusion

Methods of cleaning substrates are disclosed, particularly cleaning orremoval of titanium-containing layers from a substrate surface wherethose titanium-containing layers were formed by chemical vapordeposition (CVD) techniques. The various embodiments use sulfuric acidsolutions to remove titanium-containing layers without detrimentallyremoving surrounding materials, such as tungsten or silicon oxidematerials. The sulfuric acid solutions consist essentially of aqueous oranhydrous sulfuric acid. Integrated circuit devices produced inaccordance with embodiments of the invention have a reduced tendency forelectrical shorts caused by residual titanium-containing layers on thesurface of the substrate.

In devices where physical vapor deposition (PVD) techniques were used toform the titanium-containing layers, hydrofluoric acid (HF)-basedsolutions could be used to remove the titanium-containing layers withoutdetrimentally removing a tungsten layer. However, due to the differencesin the chemical characteristics of CVD layers, these prior cleaningsolutions are generally ineffective at removing the titanium-containinglayers. Ineffective removal of the titanium-containing layers increasesthe likelihood of metal shorts in resulting semiconductor devices.

Titanium-containing layers retained in the resultant device, where thosetitanium-containing layers were formed by CVD techniques, have improvedsurface characteristics over such titanium-containing layers exposed totraditional HF-based cleaning solutions. Such improved surfacecharacteristics are the result of more uniform removal and reducedpitting of the surface.

Piranha baths, solutions containing H₂SO₄ and H₂O₂, are generallyeffective at removing titanium-containing layers deposited by CVD orPVD, but they also tend to remove tungsten at rates too high to permitremoval of the titanium-containing layer without detrimentally removingtungsten. The embodiments of substrate cleaning methods provided hereinfacilitate selective and uniform removal of CVD titanium-containinglayers while leaving the tungsten substantially un-attacked.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptions or variations of the present invention.Therefore, it is manifestly intended that this invention be limited onlyby the claims and equivalents thereof.

1. A semiconductor die, comprising: an integrated circuit supported by abase layer and having a plurality of integrated circuit devices, whereinat least one of the plurality of integrated circuit devices has asemiconductor structure formed by a method comprising: forming aninsulator layer on the base layer, wherein the insulator layer has asurface; patterning the insulator layer to define a hole, wherein thehole has sidewalls defined by the insulator layer and a bottom definedby an exposed portion of the base layer; forming a titanium layeroverlying the surface of the insulator layer and the sidewalls andbottom of the hole by chemical vapor deposition; forming a titaniumnitride layer overlying the titanium layer by chemical vapor deposition;forming a tungsten layer overlying the titanium nitride layer andfilling the hole; removing a portion of the tungsten layer overlying thesurface of the insulator layer; and removing a portion of the titaniumand titanium nitride layers overlying the surface of the insulator layersubsequent to removing the portion of the plug layer by exposing theportion of the titanium and titanium nitride layers to a sulfuric acidsolution.
 2. A memory device, comprising: an array of memory cells,wherein at least one memory cell has a bit-line contact formed by amethod comprising: forming an insulator layer on a base layer, whereinthe insulator layer has a surface; patterning the insulator layer todefine a hole, wherein the hole has sidewalls defined by the insulatorlayer and a bottom defined by an exposed portion of the base layer;forming a titanium layer overlying the surface of the insulator layerand the sidewalls and bottom of the hole by chemical vapor deposition;forming a titanium nitride layer overlying the titanium layer bychemical vapor deposition; forming a tungsten layer overlying thetitanium nitride layer and filling the hole; removing a portion of thetungsten layer overlying the surface of the insulator layer; andremoving a portion of the titanium and titanium nitride layers overlyingthe surface of the insulator layer subsequent to removing the portion ofthe plug layer by exposing the portion of the titanium and titaniumnitride layers to a sulfuric acid solution; a row access circuit coupledto the array of memory cells; a column access circuit coupled to thearray of memory cells; and an address decoder circuit coupled to the rowaccess circuit and the column access circuit.
 3. A memory module,comprising: a support; a plurality of leads extending from the support;a command link coupled to at least one of the plurality of leads; aplurality of data links, wherein each data link is coupled to at leastone of the plurality of leads; and at least one memory device containedon the support and coupled to the command link, wherein the at least onememory device comprises: an array of memory cells, wherein at least onememory cell has a bit-line contact formed by a method comprising:forming an insulator layer on a base layer, wherein the insulator layerhas a surface; patterning the insulator layer to define a hole, whereinthe hole has sidewalls defined by the insulator layer and a bottomdefined by an exposed portion of the base layer; forming a titaniumlayer overlying the surface of the insulator layer and the sidewalls andbottom of the hole by chemical vapor deposition; forming a titaniumnitride layer overlying the titanium layer by chemical vapor deposition;forming a tungsten layer overlying the titanium nitride layer andfilling the hole; removing a portion of the tungsten layer overlying thesurface of the insulator layer; and removing a portion of the titaniumand titanium nitride layers overlying the surface of the insulator layersubsequent to removing the portion of the plug layer by exposing theportion of the titanium and titanium nitride layers to a sulfuric acidsolution; a row access circuit coupled to the array of memory cells; acolumn access circuit coupled to the array of memory cells; and anaddress decoder circuit coupled to the row access circuit and the columnaccess circuit.
 4. A memory system, comprising: a controller; a commandlink coupled to the controller; a data link coupled to the controller;and a memory device coupled to the command link and the data link,wherein the memory device comprises: an array of memory cells, whereinat least one memory cell has a bit-line contact formed by a methodcomprising: forming an insulator layer on a base layer, wherein theinsulator layer has a surface; patterning the insulator layer to definea hole, wherein the hole has sidewalls defined by the insulator layerand a bottom defined by an exposed portion of the base layer; forming atitanium layer overlying the surface of the insulator layer and thesidewalls and bottom of the hole by chemical vapor deposition; forming atitanium nitride layer overlying the titanium layer by chemical vapordeposition; forming a tungsten layer overlying the titanium nitridelayer and filling the hole; removing a portion of the tungsten layeroverlying the surface of the insulator layer; and removing a portion ofthe titanium and titanium nitride layers overlying the surface of theinsulator layer subsequent to removing the portion of the plug layer byexposing the portion of the titanium and titanium nitride layers to asulfuric acid solution; a row access circuit coupled to the array ofmemory cells; a column access circuit coupled to the array of memorycells; and an address decoder circuit coupled to the row access circuitand the column access circuit.
 5. An electronic system, comprising: aprocessor; and a circuit module having a plurality of leads coupled tothe processor, and further having a semiconductor die coupled to theplurality of leads, wherein the semiconductor die comprises: anintegrated circuit supported by a base layer and having a plurality ofintegrated circuit devices, wherein at least one of the plurality ofintegrated circuit devices has a semiconductor structure formed by amethod comprising: forming an insulator layer on a base layer, whereinthe insulator layer has a surface; patterning the insulator layer todefine a hole, wherein the hole has sidewalls defined by the insulatorlayer and a bottom defined by an exposed portion of the base layer;forming a titanium layer overlying the surface of the insulator layerand the sidewalls and bottom of the hole by chemical vapor deposition;forming a titanium nitride layer overlying the titanium layer bychemical vapor deposition; forming a tungsten layer overlying thetitanium nitride layer and filling the hole; removing a portion of thetungsten layer overlying the surface of the insulator layer; andremoving a portion of the titanium and titanium nitride layers overlyingthe surface of the insulator layer subsequent to removing the portion ofthe plug layer by exposing the portion of the titanium and titaniumnitride layers to a sulfuric acid solution.
 6. A semiconductor die,comprising: an integrated circuit supported by a base layer and having aplurality of integrated circuit devices, wherein at least one of theplurality of integrated circuit devices has a semiconductor structureformed by a method comprising: selecting a material generally resistantto sulfuric acid for use as a plug layer; depositing the plug layer overa titanium-containing layer on a surface of a substrate; removing aportion of the plug layer thereby exposing the titanium-containinglayer; and applying a solution of H₂SO₄ to the substrate surface,thereby removing at least a portion of the titanium-containing layer. 7.A semiconductor die, comprising: an integrated circuit supported by abase layer and having a plurality of integrated circuit devices, whereinat least one of the plurality of integrated circuit devices has asemiconductor structure formed by a method comprising: applying asolution of H₂SO₄ to a substrate surface, thereby removing at least aportion of a titanium-containing layer on the substrate surface; andrecessing a remaining portion of the titanium-containing layer below thesubstrate surface by immersing the substrate surface in H₂SO₄ and H₂O₂.8. A semiconductor die, comprising: an integrated circuit supported by abase layer and having a plurality of integrated circuit devices, whereinat least one of the plurality of integrated circuit devices has asemiconductor structure formed by a method comprising: cleaning atitanium-containing layer from a substrate surface, wherein a dielectricanti-reflection coating is interposed between the substrate surface andthe titanium-containing layer, and the titanium-containing layer iscleaned by applying a solution of H₂SO₄ to the substrate, therebyremoving at least a portion of the titanium-containing layer and therebyleaving at least a portion of the dielectric anti-reflection coatingsubsequent to removing a portion of a plug layer containing materialsgenerally resistant to sulfuric acid.
 9. A semiconductor die,comprising: an integrated circuit supported by a base layer and having aplurality of integrated circuit devices, wherein at least one of theplurality of integrated circuit devices has a semiconductor structureformed by a method comprising: forming an insulator layer on a baselayer, wherein the insulator layer has a surface; forming a dielectricanti-reflective coating overlying the insulator layer; patterning theinsulator layer and the dielectric anti-reflective coating to define ahole, wherein the hole has sidewalls defined by the insulator layer anda bottom defined by an exposed portion of the base layer; forming atitanium layer overlying the surface of the insulator layer and thesidewalls and bottom of the hole by chemical vapor deposition; forming atitanium nitride layer overlying the titanium layer by chemical vapordeposition; forming a tungsten layer overlying the titanium nitridelayer and filling the hole; removing a portion of the tungsten layeroverlying the surface of the insulator layer; removing a portion of thetitanium and titanium nitride layers overlying the surface of theinsulator layer subsequent to removing the portion of the tungsten layerby immersing the portion of the titanium and titanium nitride layers ina sulfuric acid solution heated to approximately 100-140° C.; andremoving the dielectric anti-reflective coating.
 10. A memory device,comprising: an array of memory cells, wherein at least one memory cellhas a bit-line contact formed by a method comprising: selecting amaterial generally resistant to sulfuric acid for use as a plug layer;depositing the plug layer over a titanium-containing layer on a surfaceof a substrate; removing a portion of the plug layer thereby exposingthe titanium-containing layer; and applying a solution of H₂SO₄ to thesubstrate surface, thereby removing at least a portion of thetitanium-containing layer; a row access circuit coupled to the array ofmemory cells; a column access circuit coupled to the array of memorycells; and an address decoder circuit coupled to the row access circuitand the column access circuit.
 11. A memory device, comprising: an arrayof memory cells, wherein at least one memory cell has a bit-line contactformed by a method comprising: applying a solution of H₂SO₄ to asubstrate surface, thereby removing at least a portion of atitanium-containing layer on the substrate surface; and recessing aremaining portion of the titanium-containing layer below the substratesurface by immersing the substrate surface in H₂SO₄ and H₂O₂; a rowaccess circuit coupled to the array of memory cells; a column accesscircuit coupled to the array of memory cells; and an address decodercircuit coupled to the row access circuit and the column access circuit.12. A memory device, comprising: an array of memory cells, wherein atleast one memory cell has a bit-line contact formed by a methodcomprising: cleaning a titanium-containing layer from a substratesurface, wherein a dielectric anti-reflection coating is interposedbetween the substrate surface and the titanium-containing layer, and thetitanium-containing layer is cleaned by applying a solution of H₂SO₄ tothe substrate, thereby removing at least a portion of thetitanium-containing layer and thereby leaving at least a portion of thedielectric anti-reflection coating subsequent to removing a portion of aplug layer containing materials generally resistant to sulfuric acid; arow access circuit coupled to the array of memory cells; a column accesscircuit coupled to the array of memory cells; and an address decodercircuit coupled to the row access circuit and the column access circuit.13. A memory device, comprising: an array of memory cells, wherein atleast one memory cell has a bit-line contact formed by a methodcomprising: forming an insulator layer on a base layer, wherein theinsulator layer has a surface; forming a dielectric anti-reflectivecoating overlying the insulator layer; patterning the insulator layerand the dielectric anti-reflective coating to define a hole, wherein thehole has sidewalls defined by the insulator layer and a bottom definedby an exposed portion of the base layer; forming a titanium layeroverlying the surface of the insulator layer and the sidewalls andbottom of the hole by chemical vapor deposition; forming a titaniumnitride layer overlying the titanium layer by chemical vapor deposition;forming a tungsten layer overlying the titanium nitride layer andfilling the hole; removing a portion of the tungsten layer overlying thesurface of the insulator layer; removing a portion of the titanium andtitanium nitride layers overlying the surface of the insulator layersubsequent to removing the portion of the tungsten layer by immersingthe portion of the titanium and titanium nitride layers in a sulfuricacid solution heated to approximately 100-140° C.; and removing thedielectric anti-reflective coating; a row access circuit coupled to thearray of memory cells; a column access circuit coupled to the array ofmemory cells; and an address decoder circuit coupled to the row accesscircuit and the column access circuit.
 14. A memory module, comprising:a support; a plurality of leads extending from the support; a commandlink coupled to at least one of the plurality of leads; a plurality ofdata links, wherein each data link is coupled to at least one of theplurality of leads; and at least one memory device contained on thesupport and coupled to the command link, wherein the at least one memorydevice comprises: an array of memory cells, wherein at least one memorycell has a bit-line contact formed by a method comprising: selecting amaterial generally resistant to sulfuric acid for use as a plug layer;depositing the plug layer over a titanium-containing layer on a surfaceof a substrate; removing a portion of the plug layer thereby exposingthe titanium-containing layer; and applying a solution of H₂SO₄ to thesubstrate surface, thereby removing at least a portion of thetitanium-containing layer; a row access circuit coupled to the array ofmemory cells; a column access circuit coupled to the array of memorycells; and an address decoder circuit coupled to the row access circuitand the column access circuit.
 15. A memory module, comprising: asupport; a plurality of leads extending from the support; a command linkcoupled to at least one of the plurality of leads; a plurality of datalinks, wherein each data link is coupled to at least one of theplurality of leads; and at least one memory device contained on thesupport and coupled to the command link, wherein the at least one memorydevice comprises: an array of memory cells, wherein at least one memorycell has a bit-line contact formed by a method comprising: applying asolution of H₂SO₄ to a substrate surface, thereby removing at least aportion of a titanium-containing layer on the substrate surface; andrecessing a remaining portion of the titanium-containing layer below thesubstrate surface by immersing the substrate surface in H₂SO₄ and H₂O₂;a row access circuit coupled to the array of memory cells; a columnaccess circuit coupled to the array of memory cells; and an addressdecoder circuit coupled to the row access circuit and the column accesscircuit.
 16. A memory module, comprising: a support; a plurality ofleads extending from the support; a command link coupled to at least oneof the plurality of leads; a plurality of data links, wherein each datalink is coupled to at least one of the plurality of leads; and at leastone memory device contained on the support and coupled to the commandlink, wherein the at least one memory device comprises: an array ofmemory cells, wherein at least one memory cell has a bit-line contactformed by a method comprising: cleaning a titanium-containing layer froma substrate surface, wherein a dielectric anti-reflection coating isinterposed between the substrate surface and the titanium-containinglayer, and the titanium-containing layer is cleaned by applying asolution of H₂SO₄ to the substrate, thereby removing at least a portionof the titanium-containing layer and thereby leaving at least a portionof the dielectric anti-reflection coating subsequent to removing aportion of a plug layer containing materials generally resistant tosulfuric acid; a row access circuit coupled to the array of memorycells; a column access circuit coupled to the array of memory cells; andan address decoder circuit coupled to the row access circuit and thecolumn access circuit.
 17. A memory module, comprising: a support; aplurality of leads extending from the support; a command link coupled toat least one of the plurality of leads; a plurality of data links,wherein each data link is coupled to at least one of the plurality ofleads; and at least one memory device contained on the support andcoupled to the command link, wherein the at least one memory devicecomprises: an array of memory cells, wherein at least one memory cellhas a bit-line contact formed by a method comprising: forming aninsulator layer on a base layer, wherein the insulator layer has asurface; forming a dielectric anti-reflective coating overlying theinsulator layer; patterning the insulator layer and the dielectricanti-reflective coating to define a hole, wherein the hole has sidewallsdefined by the insulator layer and a bottom defined by an exposedportion of the base layer; forming a titanium layer overlying thesurface of the insulator layer and the sidewalls and bottom of the holeby chemical vapor deposition; forming a titanium nitride layer overlyingthe titanium layer by chemical vapor deposition; forming a tungstenlayer overlying the titanium nitride layer and filling the hole;removing a portion of the tungsten layer overlying the surface of theinsulator layer; removing a portion of the titanium and titanium nitridelayers overlying the surface of the insulator layer subsequent toremoving the portion of the tungsten layer by immersing the portion ofthe titanium and titanium nitride layers in a sulfuric acid solutionheated to approximately 100-140° C.; and removing the dielectricanti-reflective coating; a row access circuit coupled to the array ofmemory cells; a column access circuit coupled to the array of memorycells; and an address decoder circuit coupled to the row access circuitand the column access circuit.
 18. A memory system, comprising: acontroller; a command link coupled to the controller; a data linkcoupled to the controller; and a memory device coupled to the commandlink and the data link, wherein the memory device comprises: an array ofmemory cells, wherein at least one memory cell has a bit-line contactformed by a method comprising: selecting a material generally resistantto sulfuric acid for use as a plug layer; depositing the plug layer overa titanium-containing layer on a surface of a substrate; removing aportion of the plug layer thereby exposing the titanium-containinglayer; and applying a solution of H₂SO₄ to the substrate surface,thereby removing at least a portion of the titanium-containing layer; arow access circuit coupled to the array of memory cells; a column accesscircuit coupled to the array of memory cells; and an address decodercircuit coupled to the row access circuit and the column access circuit.19. A memory system, comprising: a controller; a command link coupled tothe controller; a data link coupled to the controller; and a memorydevice coupled to the command link and the data link, wherein the memorydevice comprises: an array of memory cells, wherein at least one memorycell has a bit-line contact formed by a method comprising: applying asolution of H₂SO₄ to a substrate surface, thereby removing at least aportion of a titanium-containing layer on the substrate surface; andrecessing a remaining portion of the titanium-containing layer below thesubstrate surface by immersing the substrate surface in H₂SO₄ and H₂O₂;a row access circuit coupled to the array of memory cells; a columnaccess circuit coupled to the array of memory cells; and an addressdecoder circuit coupled to the row access circuit and the column accesscircuit.
 20. A memory system, comprising: a controller; a command linkcoupled to the controller; a data link coupled to the controller; and amemory device coupled to the command link and the data link, wherein thememory device comprises: an array of memory cells, wherein at least onememory cell has a bit-line contact formed by a method comprising:cleaning a titanium-containing layer from a substrate surface, wherein adielectric anti-reflection coating is interposed between the substratesurface and the titanium-containing layer, and the titanium-containinglayer is cleaned by applying a solution of H₂SO₄ to the substrate,thereby removing at least a portion of the titanium-containing layer andthereby leaving at least a portion of the dielectric anti-reflectioncoating subsequent to removing a portion of a plug layer containingmaterials generally resistant to sulfuric acid; a row access circuitcoupled to the array of memory cells; a column access circuit coupled tothe array of memory cells; and an address decoder circuit coupled to therow access circuit and the column access circuit.
 21. A memory system,comprising: a controller; a command link coupled to the controller; adata link coupled to the controller; and a memory device coupled to thecommand link and the data link, wherein the memory device comprises: anarray of memory cells, wherein at least one memory cell has a bit-linecontact formed by a method comprising: forming an insulator layer on abase layer, wherein the insulator layer has a surface; forming adielectric anti-reflective coating overlying the insulator layer;patterning the insulator layer and the dielectric anti-reflectivecoating to define a hole, wherein the hole has sidewalls defined by theinsulator layer and a bottom defined by an exposed portion of the baselayer; forming a titanium layer overlying the surface of the insulatorlayer and the sidewalls and bottom of the hole by chemical vapordeposition; forming a titanium nitride layer overlying the titaniumlayer by chemical vapor deposition; forming a tungsten layer overlyingthe titanium nitride layer and filling the hole; removing a portion ofthe tungsten layer overlying the surface of the insulator layer;removing a portion of the titanium and titanium nitride layers overlyingthe surface of the insulator layer subsequent to removing the portion ofthe tungsten layer by immersing the portion of the titanium and titaniumnitride layers in a sulfuric acid solution heated to approximately100-140° C.; and removing the dielectric anti-reflective coating; a rowaccess circuit coupled to the array of memory cells; a column accesscircuit coupled to the array of memory cells; and an address decodercircuit coupled to the row access circuit and the column access circuit.22. An electronic system, comprising: a processor; and a circuit modulehaving a plurality of leads coupled to the processor, and further havinga semiconductor die coupled to the plurality of leads, wherein thesemiconductor die comprises: an integrated circuit supported by a baselayer and having a plurality of integrated circuit devices, wherein atleast one of the plurality of integrated circuit devices has asemiconductor structure formed by a method comprising: selecting amaterial generally resistant to sulfuric acid for use as a plug layer;depositing the plug layer over a titanium-containing layer on a surfaceof a substrate; removing a portion of the plug layer thereby exposingthe titanium-containing layer; and applying a solution of H₂SO₄ to thesubstrate surface, thereby removing at least a portion of thetitanium-containing layer.
 23. An electronic system, comprising: aprocessor; and a circuit module having a plurality of leads coupled tothe processor, and further having a semiconductor die coupled to theplurality of leads, wherein the semiconductor die comprises: anintegrated circuit supported by a base layer and having a plurality ofintegrated circuit devices, wherein at least one of the plurality ofintegrated circuit devices has a semiconductor structure formed by amethod comprising: applying a solution of H₂SO₄ to a substrate surface,thereby removing at least a portion of a titanium-containing layer onthe substrate surface; and recessing a remaining portion of thetitanium-containing layer below the substrate surface by immersing thesubstrate surface in H₂SO₄ and H₂O₂.
 24. An electronic system,comprising: a processor; and a circuit module having a plurality ofleads coupled to the processor, and further having a semiconductor diecoupled to the plurality of leads, wherein the semiconductor diecomprises: an integrated circuit supported by a base layer and having aplurality of integrated circuit devices, wherein at least one of theplurality of integrated circuit devices has a semiconductor structureformed by a method comprising: cleaning a titanium-containing layer froma substrate surface, wherein a dielectric anti-reflection coating isinterposed between the substrate surface and the titanium-containinglayer, and the titanium-containing layer is cleaned by applying asolution of H₂SO₄ to the substrate, thereby removing at least a portionof the titanium-containing layer and thereby leaving at least a portionof the dielectric anti-reflection coating subsequent to removing aportion of a plug layer containing materials generally resistant tosulfuric acid.
 25. An electronic system, comprising: a processor; and acircuit module having a plurality of leads coupled to the processor, andfurther having a semiconductor die coupled to the plurality of leads,wherein the semiconductor die comprises: an integrated circuit supportedby a base layer and having a plurality of integrated circuit devices,wherein at least one of the plurality of integrated circuit devices hasa semiconductor structure formed by a method comprising: forming aninsulator layer on a base layer, wherein the insulator layer has asurface; forming a dielectric anti-reflective coating overlying theinsulator layer; patterning the insulator layer and the dielectricanti-reflective coating to define a hole, wherein the hole has sidewallsdefined by the insulator layer and a bottom defined by an exposedportion of the base layer; forming a titanium layer overlying thesurface of the insulator layer and the sidewalls and bottom of the holeby chemical vapor deposition; forming a titanium nitride layer overlyingthe titanium layer by chemical vapor deposition; forming a tungstenlayer overlying the titanium nitride layer and filling the hole;removing a portion of the tungsten layer overlying the surface of theinsulator layer; removing a portion of the titanium and titanium nitridelayers overlying the surface of the insulator layer subsequent toremoving the portion of the tungsten layer by immersing the portion ofthe titanium and titanium nitride layers in a sulfuric acid solutionheated to approximately 100-140° C.; and removing the dielectricanti-reflective coating.